The present invention relates to wireless communication systems, and, more specifically to wireless communication systems using various modulation techniques.
Gaussian minimum shift keying (“GMSK”) is a popular modulation technique due to its simplicity and bandwidth efficiency. A popular technique for generating GMSK signals is “direct modulation” in which the modulation is performed directly in the frequency synthesizer. However, one drawback of direct modulation is that it is difficult to maintain adequate control over the modulation index and the filter bandwidth because of variations in the analog circuitry and the effects of tuning the synthesizer to different center frequencies. Designing a transmitter that can maintain a near-ideal minimum shift keying (“MSK”) modulation index (e.g., by generating the baseband modulation in a digital signal processor) generally results in additional cost, complexity and power consumption. Thus, a demodulator for which performance is insensitive to modulation index is desired.